Cache Octicon SVGs for same icon/options combination

docs/content/packages/rails.mdx

@@ -23,3 +23,7 @@ This rails helper lets you easily include svg octicons in your rails apps.
     ```
 
 We recommend including the CSS in the [`@primer/octicons`](/packages/javascript) npm module. You can also npm install that package and include `build/build.css` in your styles.
+
+## Caching
+
+`octicons_helper` caches repeated calls to `octicon` based on the name of the icon and the provided `options` hash. Avoid arbitrary/high cardinality `options` (such as an `id` with a unique record identifier), as they can cause a memory leak.

lib/octicons_helper/lib/octicons_helper/helper.rb

@@ -2,13 +2,23 @@
 require "action_view"
 
 module OcticonsHelper
-
   include ActionView::Helpers::TagHelper
 
+  mattr_accessor :octicons_helper_cache, default: {}
+
   def octicon(symbol, options = {})
     return "" if symbol.nil?
 
-    icon = Octicons::Octicon.new(symbol, options)
-    content_tag(:svg, icon.path.html_safe, icon.options) # rubocop:disable Rails/OutputSafety
+    cache_key = [symbol, options].to_s
+
+    if octicons_helper_cache[cache_key]
+      octicons_helper_cache[cache_key]
+    else
+      icon = Octicons::Octicon.new(symbol, options)
+
+      tag = content_tag(:svg, icon.path.html_safe, icon.options).freeze # rubocop:disable Rails/OutputSafety
+      octicons_helper_cache[cache_key] = tag
+      tag
+    end
   end
 end

lib/octicons_helper/test/octicons_helper_test.rb

@@ -17,5 +17,27 @@
     it "adds html attributes to output" do
       assert_match /foo="bar"/, octicon("alert", foo: "bar")
     end
+
+    it "caches SVGs for two calls with the same arguments" do
+      OcticonsHelper.octicons_helper_cache = {}
+
+      mock = Minitest::Mock.new
+      def mock.path
+        @@call_count ||= 0
+        @@call_count += 1
+
+        raise "Octicon library called twice" if @@call_count > 1
+
+        "foo"
+      end
+      def mock.options; end
+
+      Octicons::Octicon.stub :new, mock do
+        octicon("alert")
+        octicon("alert")
+      end
+
+      OcticonsHelper.octicons_helper_cache = {}
+    end
   end
 end